<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
    .container{
        display:flex;
        background-color: yellow;
        width:800px;
        height:300px;
    }
    .item{
        width:100px;
        height:100px;
        background-color:red;
        border:1px solid blue;
    }
    
    </style>
</head>
<body>
    <div>
        <div class="item">123</div>
        <div class="item">456</div>
        <div class="item">789</div>
    </div>
</body>
</html>